CamonWheels is offering up some new V-Groove roller wheels for under $8 bucks shipped. Images show the grooved wheels fitting on 15mm rods, 1/4″ rod, and 1″ PVC. The overall OD of the wheel (outside diameter) is at 1″. If you were to build a track dolly of sorts, the V-Groove or U-groove type wheels will help keep them on track.

I bought two sets of these and just received them a couple days ago. They are a bit smaller then I was expecting but will work pretty well. The orange portion is a hard plastic. The bearing is not abec rated but is pretty smooth. The bearing is 18mm with a bore of 7mm. All in all they are pretty nice for the price.

Maybe these are of better quality, but I’ve bought a similar wheels a year back from ebay, but the bearing was terrible and had such a big side lash (you were able to tilt the bearing at least 5-6 degrees)
That made the whole thing unusable.